Articles
CRITICAL N-CONCENTRATIONS IN BROCCOLI AND CAULIFLOWER, EVALUATED IN FIELD TRIALS WITH VARYING LEVELS AND TIMING N FERTILIZER
Article number
627_31
Pages
241 – 249
Language
English
Abstract
Seven field trials were carried out on loam soil in the period 1999-2001 to assess optimum levels and timing of N application, and to obtain data on critical N% in plants.
Measurements of N content were made in both harvested products and crop residues.
The results showed no benefit of increasing N supply beyond 150 kg ha-1 in broccoli or white cauliflower, but 250 kg ha– 1 gave highest yield of green cauliflower (Romanesco).
The latter crop had a longer growth period, and may have experienced greater leaching.
Split application of N fertilizer was beneficial to all three crops, relative to giving all at planting.
N recoveries declined with increasing N supply in all crops, and were lowest in green cauliflower.
Split application gave only slightly increases in N recovery.
Much of the N taken up by plants remained in the crop residues after harvest (normally 50-75%).
In these trials the N concentration in the whole plant at harvest was, on fertilized plots, slightly higher than the critical N% for arable crops, but considerably below that which has been proposed specifically for brassica crops (Greenwood et al.1996). In other trials N concentrations measured at frequent intervals in the growing season, were seen to follow the critical N curve for arable crops when fertilizer was applied only at planting, but to be intermediate between the two critical N curves when N application was spread over a six week period.
There may be some justification for recommending higher plant N levels in flowering brassicas than in leafy ones such as cabbage, but the topic requires more research.
Increasing the N supply reduces its use efficiency under all conditions.
Measurements of N content were made in both harvested products and crop residues.
The results showed no benefit of increasing N supply beyond 150 kg ha-1 in broccoli or white cauliflower, but 250 kg ha– 1 gave highest yield of green cauliflower (Romanesco).
The latter crop had a longer growth period, and may have experienced greater leaching.
Split application of N fertilizer was beneficial to all three crops, relative to giving all at planting.
N recoveries declined with increasing N supply in all crops, and were lowest in green cauliflower.
Split application gave only slightly increases in N recovery.
Much of the N taken up by plants remained in the crop residues after harvest (normally 50-75%).
In these trials the N concentration in the whole plant at harvest was, on fertilized plots, slightly higher than the critical N% for arable crops, but considerably below that which has been proposed specifically for brassica crops (Greenwood et al.1996). In other trials N concentrations measured at frequent intervals in the growing season, were seen to follow the critical N curve for arable crops when fertilizer was applied only at planting, but to be intermediate between the two critical N curves when N application was spread over a six week period.
There may be some justification for recommending higher plant N levels in flowering brassicas than in leafy ones such as cabbage, but the topic requires more research.
Increasing the N supply reduces its use efficiency under all conditions.
Authors
H. Riley, I. Vågen
Keywords
Brassica oleracea var. italica and var. botrytis, Critical N%, N fertilizer amount, N fertilizer timing, Residues, Yield
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